Recently, calls for higher performances such as high-definition (high-vision) displays and flat panel displays have grown in the field of displays. In response to these calls, various research and development are being made.
Typical flat panel displays are liquid crystal displays (LCDs) and plasma display panels (PDPs). Particularly, PDPs are thin and suitable for large-scale screens, with products using 50-inch class PDPs having already been developed.
PDPs can roughly be divided into two types: direct current (DC) type; and alternating current (AC) type. The present mainstream is AC-type PDPs that are suitable for being made larger in size.
In general, PDPs are constructed of phosphor cells of respective colors arranged in matrix. As one example, Japanese Laid-Open Patent Application No. 9-35628 discloses an AC surface-discharge type PDP. This PDP has the following panel construction. A front glass substrate and a back glass substrate are arranged in parallel with barrier ribs interposed between them. On the front glass substrate, pairs of display electrodes (scanning electrodes and sustaining electrodes) are formed in parallel. These electrodes are covered with a dielectric layer. On the back glass substrate, address electrodes are formed so as to face the scanning electrodes at right angles. Phosphor layers of respective colors (red, green, and blue) are formed in spaces divided by the barrier ribs between the front and back substrates. A discharge gas is enclosed in the spaces to form cells that emit red, green and blue light. By a driving circuit applying voltage to each electrode, discharge occurs and ultraviolet rays are emitted. Phosphor particles (red, green, and blue) in the phosphor layers are excited with these ultraviolet rays to emit light, resulting in a luminescent display.
In the PDP described above, glass plates manufactured from a sodium borosilicate glass material using a float method are typically used for the front glass substrate and the back glass substrate. For the display electrodes and the address electrodes, Cr—Cu—Cr (chromium-copper-chromium) electrodes are sometimes used, and silver electrodes that are relatively cheap are often used.
In general, the silver electrodes are formed using a thick-film forming method. To be more specific, a silver paste made of Ag particles, a glass frit, resin, solvent, and the like is applied as a pattern using a screen-printing method. Alternatively, a film made of Ag particles, a glass frit, resin, and the like is applied using a lamination method and is patterned. In either case, the applied paste or the applied film is baked at the temperature of 500° C. or higher to fuse Ag particles together for improving conductivity as well as to remove resin.
The dielectric layer is usually formed by applying a paste made of powdered lead glass with a low melting point or the like and resin, using the screen-printing method, a die coat method, the lamination method, or the like, and baking the applied paste at the temperature of 500° C. or higher.
The PDP using such silver electrodes as described above is known to have the following problem. From the silver electrodes, Ag diffuses as ions into the glass substrate and the dielectric layer. The diffused Ag ions are reduced to generate Ag colloids. Due to this, the glass substrate and the dielectric layer yellow easily. This yellowing causes a decrease in the color temperature of full-white images when the PDP is driven, deteriorating image quality of the PDP.
This yellowing of the glass substrate and the dielectric layer causes deterioration in the luminance of blue cells and a decrease in the color temperature of full-white images.
To solve this yellowing problem in the PDP, as one example, Japanese Laid-Open Patent Application No. 10-255669 discloses a technique for abrading a surface layer with a thickness of 1 μm to 1000 μm of a glass substrate, by mechanically polishing the surface of the glass substrate.
This technique is considered effective in preventing the yellowing of the glass substrate. However, it is extremely difficult to uniformly abrade 1 μm or thicker surface part of such a large glass substrate that is used in the PDP in a short period of time. For example, it takes at least several tens minutes to abrade the 1 μm-thick surface part of the glass substrate with an Oskar-type polishing device. Furthermore, by abrading 1 μm or thicker surface part of the glass substrate, the thickness of the glass substrate as a whole may become uneven.
Accordingly, new solutions to the yellowing in the PDP that use the silver electrodes are being sought.